To get back to your original question about how an increase in stroke affects ignition timing, I'm not sure if you've seen the following webpage: http://www.jcna.com/library/tech/tech0013.html. It lists various things that affect timing.
As RON98 mentioned, the flame front travels faster the higher the compression ratio. Therefore, all else being equal, the higher the compression ratio, the less ignition advance you should have in order to avoid detonation. When you increase the stroke of an engine, you increase the speed at which the piston is traveling and decrease the amount of time it is spending at top dead center. Since the compression ratio is highest at top dead center, the engine reaches that compression ratio for a shorter period of time. At the lower compression ratios around TDC that a longer stroke engine will have, the flame front will travel slower. So, all else being equal, a longer stroke engine will need more ignition advance than the standard engine.
However, if you change not only the stroke but anything else as well (compression ratio, piston top shape, rod length, etc.) all bets are off as to what the net effect on the timing will be. In any case, it should be tuned on a dyno.
Now as to the relative merits of a stand-alone EMS custom programmed on a dyno vs. a chip for the Honda EMS custom programmed on a dyno...
As RON98 mentioned, the flame front travels faster the higher the compression ratio. Therefore, all else being equal, the higher the compression ratio, the less ignition advance you should have in order to avoid detonation. When you increase the stroke of an engine, you increase the speed at which the piston is traveling and decrease the amount of time it is spending at top dead center. Since the compression ratio is highest at top dead center, the engine reaches that compression ratio for a shorter period of time. At the lower compression ratios around TDC that a longer stroke engine will have, the flame front will travel slower. So, all else being equal, a longer stroke engine will need more ignition advance than the standard engine.
However, if you change not only the stroke but anything else as well (compression ratio, piston top shape, rod length, etc.) all bets are off as to what the net effect on the timing will be. In any case, it should be tuned on a dyno.
Now as to the relative merits of a stand-alone EMS custom programmed on a dyno vs. a chip for the Honda EMS custom programmed on a dyno...
Last edited: